README: update subscribe information

Majordomo commands are no longer supported after the migration away from
legacy vger infrastructure.

https://subspace.kernel.org/vger.kernel.org.html#what-happened-to-majordomo

Reported-by: Kalevi Kolttonen <[email protected]>
Signed-off-by: Petr Lautrbach <[email protected]>
Acked-by: James Carter <[email protected]>

Author: bachradsusi

README.md

@@ -16,9 +16,8 @@ and system libraries which allow for the configuration and management of an
 SELinux-based system.
 
 Please submit all bug reports and patches to the <[email protected]>
-mailing list. You can subscribe by sending "subscribe selinux" in the body of
-an email to <[email protected]>. Archives of the mailing list are
-available at https://lore.kernel.org/selinux.
+mailing list. You can subscribe by sending an email to <[email protected]>
+Archives of the mailing list are available at https://lore.kernel.org/selinux.
 
 Installation
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